Asphalt composition, method for producing same and additive for asphalt

ABSTRACT

The asphalt composition contains asphalt and cellulose, wherein the content of the cellulose is 0.01 part by mass or more and 10 parts by mass or less based on 100 parts by mass of the asphalt, and a crystallization index of the cellulose is 50% or less.

FIELD OF THE INVENTION

The present invention relates to an asphalt composition and a method forproducing the same, and to an additive for asphalt.

BACKGROUND OF THE INVENTION

An asphalt pavement using an asphalt mixture has been performed forpaving driveways, parking spaces, cargo yards, sidewalks, etc., becauseof relatively easy construction and a short period of time frombeginning of paving works to traffic start.

The asphalt pavement includes a road surface that is formed of anasphalt mixture containing aggregates bonded with each other throughasphalt, and hence, paved roads exhibit good hardness and gooddurability.

However, this asphalt pavement involved such a problem that itdeteriorates over time, resulting in the occurrence of rutting orcracking.

For the purpose of reducing an environmental load while inhibiting theoccurrence of rutting on a pavement surface, PTL 1 (JP 2011-111712 A)discloses an asphalt concrete composition for pavement composed of anasphalt mixture and a plant fiber body, in which the plant fiber body isa kenaf fiber or a kenaf fiber-made mesh sheet.

In addition, for the purpose of providing an asphalt composition havingimproved flow resistance, abrasion resistance, and crack resistance ofthe asphalt, PTL 2 (JP 2001-158857 A) discloses an asphalt compositioncontaining asphalt and a hydrophobized cellulose fiber.

SUMMARY OF THE INVENTION

The present invention is concerned with an asphalt compositioncontaining asphalt and cellulose, wherein the content of the celluloseis 0.01 part by mass or more and 10 parts by mass or less based on 100parts by mass of the asphalt, and a crystallization index of thecellulose is 50% or less.

DETAILED DESCRIPTION OF THE INVENTION [Asphalt Composition]

The asphalt composition of the present invention contains asphalt andcellulose, wherein the content of the cellulose is 0.01 part by mass ormore and 10 parts by mass or less based on 100 parts by mass of theasphalt, and a crystallization index of the cellulose is 50% or less.The cellulose having a crystallization index of 50% or less ishereinafter also referred to as “amorphous cellulose”.

The present invention is to provide an asphalt composition enabling oneto provide an asphalt pavement in which the occurrence of rutting andfatigue cracking is inhibited and a method for producing the same, andalso to provide an additive for asphalt.

The present inventors have found that when the asphalt compositioncontains a specified amount of amorphous cellulose, a crystallizationindex of which is a specified value, the occurrence of rutting andfatigue cracking of the asphalt pavement obtained by using the asphaltcomposition is inhibited.

Although a detailed mechanism in which the effect of the presentinvention is obtained is not elucidated yet, a part thereof may beconsidered as follows. That is, in order to improve the mechanicalstrength, it has hitherto been performed to add a reinforced fiber toasphalt. In the present invention, it may be presumed that by usingcellulose not having a strong crystal structure and having a lowcrystallization index, dispersibility of the cellulose in the asphaltcomposition is improved, whereby the mechanical properties, such asrutting resistance and fatigue cracking resistance, are improved.

The “rutting” means unevenness that is continuously generated in thelongitudinal direction in the road driving portion when at a hightemperature in the season of summer or the like, an asphalt layerforming the pavement surface flows. The rutting correlates with theplastic flow resistance of the asphalt composition that is a binder ofthe asphalt pavement, and according to the binder standards of SUPERPAVE(Japan Road Association, “Manual for Test Method of Pavement (SeparateVolume)”, 1996), it is possible to evaluate the rutting in terms ofG*/sin δ of the asphalt composition (binder). Here, G* represents acomplex modulus of elasticity, and G* and sin δ are measured with arheometer.

In view of the fact that the larger the value of G*/sin δ, the largerthe plastic flow resistance is, it is evaluated that the asphaltpavement with excellent rutting resistance can be provided by theforegoing asphalt composition.

Meanwhile, the “fatigue cracking” is a phenomenon in which the pavementsurface is cracked owing to a repeated load. According to the binderstandards of SUPERPAVE (Japan Road Association, “Manual for Test Methodof Pavement (Separate Volume)”, 1996), it is possible to evaluate thefatigue cracking resistance in terms of G*sin δ of the asphaltcomposition (binder). Here, G* represents a complex modulus ofelasticity, and G* and sin δ are measured with a rheometer.

In view of the fact that the smaller the value of G*sin δ, the largerthe fatigue cracking resistance is, it is evaluated that the asphaltpavement with excellent fatigue cracking resistance can be provided bythe foregoing asphalt composition.

In the following description, the fact that the viscoelasticity of theasphalt composition is improved means that the G*sin δ becomes smallwith an increase of the value of G*/sin δ.

In accordance with the present invention, an asphalt compositionenabling one to provide the asphalt pavement in which the occurrence ofrutting and fatigue cracking is inhibited and a method for producing thesame, and also to provide an additive for asphalt.

<Asphalt>

The asphalt composition of the present invention contains asphalt.

As the asphalt that is used in the present invention, various kinds ofasphalts can be used. Examples thereof include in addition to a straightasphalt that is petroleum asphalt for pavement, modified asphalts.

The straight asphalt as referred to herein refers to a residualbituminous material obtained by treating a crude oil with an atmosphericdistillation apparatus, a vacuum distillation apparatus, or the like.

Examples of the modified asphalt include blown asphalt; and apolymer-modified asphalt modified with a polymer material, such as athermoplastic elastomer and a thermoplastic resin (hereinafter alsoreferred to simply as “polymer-modified asphalt”).

Examples of the thermoplastic elastomer include astyrene/butadiene/styrene block copolymer (SBS), astyrene/isoprene/styrene block copolymer (SIS), and an ethylene/vinylacetate copolymer (EVA).

Examples of the thermoplastic resin include an ethylene/ethyl acrylatecopolymer, a polyolefin, such as polyethylene and polypropylene, and apolymer having a polar group and a polyolefin chain.

In the present invention, the asphalt is preferably one selected from astraight asphalt and a polymer-modified asphalt; more preferably apolymer-modified asphalt; and still more preferably a polymer-modifiedasphalt containing a polymer having a polar group and a polyolefingroup, namely one modified with a polymer having a polar group and apolyolefin chain.

In the polymer having a polar group and a polyolefin chain (hereinafteralso referred to as “modifier”), in view of the fact that the polyolefinchain moiety thereof has an affinity with the straight asphalt, whereasthe polar chain moiety thereof interacts with amorphous cellulose toreveal an affinity, it may be considered that an affinity between theamorphous cellulose and the asphalt is improved, and viscoelasticity ofthe asphalt composition is improved.

Examples of the polar group include an organic isocyanate group, an(anhydrous) carboxylic acid group, a carboxylic acid halide group, anamino group, a hydroxy group, and an epoxy group. Of these, from theviewpoint of enhancing the affinity with the amorphous cellulose, an(anhydrous) carboxylic acid group and an epoxy group are preferred, andan (anhydrous) carboxylic acid group is more preferred. The “(anhydrous)carboxylic acid group” is a general term of a carboxylic anhydride groupand a carboxylic acid group (carboxy group). Specifically, examplesthereof include polar groups derived from maleic anhydride, maleic acid,or glycidyl (meth)acrylate.

Preferred examples of the polyolefin chain include polymer chainsderived from an ethylene-based polymer (for example, high-densitypolyethylene, medium-density polyethylene, low-density polyethylene, anda copolymer of ethylene and at least one other vinyl compound (forexample, an α-olefin, vinyl acetate, methacrylic acid, and acrylicacid), a propylene-based polymer (for example, polypropylene and acopolymer of propylene and at least one other vinyl compound), anethylene/propylene copolymer, polybutene, or poly-4-methylpentene-1.Polymer chains derived from an ethylene-based polymer or apropylene-based polymer are more preferred.

Examples of the polymer having a polar group and a polyolefin chaininclude a maleic anhydride-modified polyolefin.

As the polymer having a polar group and a polyolefin chain, commerciallyavailable products may be used. Suitable examples of the commerciallyavailable product include “BONDFAST 7M” (a copolymer of ethylene andglycidyl methacrylate), manufactured by Sumitomo Chemical Co., Ltd.;“REXPEARL ET Series” (a copolymer of ethylene, (meth)acrylic acid and/orits ester, and maleic anhydride), manufactured by Japan PolyethyleneCorporation; “MODIPER A4000 Series” (a graft copolymer in which a mainchain thereof is a copolymer of ethylene and glycidyl methacrylate),manufactured by NOF Corporation; “UMEX” (maleic anhydride-modifiedpolypropylene), manufactured by Sanyo Chemical Industries, Ltd.;“OREVAC” (maleic anhydride-modified polyethylene or maleicanhydride-modified polypropylene), manufactured by Arkema Inc.;“LOTADER” (a copolymer of ethylene, an acrylic acid ester, and glycidylmethacrylate), manufactured by Arkema Inc.; “BONDINE” (a copolymer ofethylene, an acrylic acid ester, and maleic anhydride), manufactured byArkema Inc.; “KAYABRID” (maleic anhydride-modified polypropylene),manufactured by Kayaku Akzo Co., Ltd.; “NUCREL” (a copolymer of ethyleneand methacrylic acid), manufactured by Du Pont-Mitsui Polychemicals Co.,Ltd.; and “PRIMACOR” (a copolymer of ethylene and acrylic acid),manufactured by The Dow Chemical Company.

Of these, from the viewpoint of improving the viscoelasticity of theasphalt composition, the modifier is preferably a maleicanhydride-modified polyolefin, more preferably at least one selectedfrom maleic anhydride-modified polyethylene and maleicanhydride-modified polypropylene, still more preferably maleicanhydride-modified polypropylene or maleic anhydride-modifiedpolyethylene, and yet still more preferably maleic anhydride-modifiedpolypropylene.

From the viewpoint of enhancing the affinity between the amorphouscellulose and the asphalt, a weight average molecular weight of themaleic anhydride-modified polyolefin, preferably maleicanhydride-modified polyethylene or maleic anhydride-modifiedpolypropylene, is preferably 1,000 or more, more preferably 5,000 ormore, still more preferably 10,000 or more, and yet still morepreferably 30,000 or more, and it is preferably 1,000,000 or less, morepreferably 500,000 or less, still more preferably 300,000 or less, andyet still more preferably 100,000 or less.

From the viewpoint of enhancing the affinity between the amorphouscellulose and the asphalt, an acid value of the maleicanhydride-modified polyolefin, preferably maleic anhydride-modifiedpolyethylene or maleic anhydride-modified polypropylene, is preferably 1mgKOH/g or more, more preferably 2 mgKOH/g or more, still morepreferably 3 mgKOH/g or more, yet still more preferably 5 mgKOH/g ormore, and even yet still more preferably 10 mgKOH/g or more, and it ispreferably 200 mgKOH/g or less, more preferably 100 mgKOH/g or less,still more preferably 60 mgKOH/g or less, and yet still more preferably30 mgKOH/g or less.

In the case where the asphalt is a polymer-modified asphalt containing apolymer (modifier) having a polar group and a polyolefin chain, and fromthe viewpoint of improving the dispersibility of the amorphous cellulosein the asphalt composition and improving the viscoelasticity of theasphalt composition, the amount of the modifier added to the straightasphalt is preferably 0.1 parts by mass or more, more preferably 0.3parts by mass or more, still more preferably 0.5 parts by mass or more,and yet still more preferably 0.8 parts by mass or more, and it ispreferably 20 parts by mass or less, more preferably 10 parts by mass orless, still more preferably 5 parts by mass or less, and yet still morepreferably 2 parts by mass or less, based on 100 parts by mass of thestraight asphalt.

<Amorphous Cellulose>

The asphalt composition of the present invention contains cellulose(amorphous cellulose) having a crystallization index of 50% or less.When the crystallization index of the cellulose is more than 50%, thecellulose has a strong crystal structure, and the effect of improvingthe viscoelasticity of the asphalt composition is not satisfactory.

In the present invention, the crystallization index of the cellulose isa crystallization index of type I cellulose calculated from adiffraction intensity value by the X-ray crystal diffraction methodaccording to the Segal method and is defined by the following expression(A).

Crystallization index of cellulose(%)=[(I _(22.6) ·I _(18.5))/I_(22.6)]×100(A)

In the expression (A), I_(22.6) represents a diffraction intensity of alattice plane (002 plane) in the X-ray diffraction (diffraction angle2θ=22.6°), and I_(18.5) represents a diffraction intensity of anamorphous part (diffraction angle 2θ=) 18.5°.

In this specification, cellulose having a crystallization index of 50%or less is occasionally referred to as “amorphous cellulose”, whereascellulose having a crystallization index of more than 50% isoccasionally referred to as “crystalline cellulose”. The “type Icellulose” refers to a crystal form of natural cellulose. Thecrystallization index of the type I cellulose is also related tophysical properties and chemical properties of the cellulose, and as itsvalue is large, hardness and density and the like increase, butelongation, flexibility, and chemical reactivity are lowered.

The crystallization index of the cellulose that is used in the presentinvention is 50% or less, and from the viewpoint of more improving theviscoelasticity of the asphalt composition, it is preferably 45% orless, and more preferably 40% or less. According to the crystallizationindex of the type I cellulose as defined by the expression (A), thoughthere is a case where the calculated value becomes minus, in the casewhere the calculated value becomes minus, the crystallization index ofthe type I cellulose is defined as 0%. In consequence, thecrystallization index of the cellulose that is used in the presentinvention is 0% or more, and from the viewpoint of rutting resistanceand fatigue cracking resistance, it is preferably 1% or more, and morepreferably 10% or more. In addition, though a combination of two or morekinds of celluloses having a different crystallization index from eachother may be used, the crystallization index of the cellulose in thatcase means a crystallization index determined from a weighted average ofthe celluloses to be used, and it is preferred that a value thereoffalls within the aforementioned range.

Although the amorphous cellulose is not particularly limited so long asits crystallization index is 50% or less, for example, celluloseobtained by subjecting a cellulose-containing raw material to amechanical treatment or the like as mentioned later is preferred.

The cellulose-containing raw material is not particularly limited, andrespective sites of plants, such as trunk, branch, leaf, stem, root,seed, and fruit, for example, plant stems and leafs, such as rice strawand corn stem; and plant shells, such as rice husk, palm shell, andcoconut shell, can be used. In addition, pulps, such as wood pulpsmanufactured from lumber from thinning, pruned branch, various woodchips, wood pulp manufactured from wood, and cotton linter pulp obtainedfrom fibers around cotton seeds; papers, such as newspaper, cardboard,magazine, and wood-free paper, may be used. However, pulps are preferredfrom the viewpoint of obtaining less colored amorphous cellulose.Furthermore, regenerated pulps and regenerated papers obtained byregenerating paper (wastepaper), such as newspaper, cardboard, magazine,and wood-free paper can also be used.

In addition, as the cellulose-containing raw material, commerciallyavailable crystalline cellulose can be used. Examples of thecommercially available crystalline cellulose include KC FLOCK(manufactured by Nippon Paper Chemical Co., Ltd.) and CEOLUS(manufactured by Asahi Kasei Chemicals Corporation).

The form of such a cellulose-containing raw material is not particularlylimited, and various forms, such as a chip form and a sheet form, can beused. The crystallization index of the type I cellulose of commerciallyavailable pulp is typically 80% or more, and the crystallization indexof the type I cellulose of commercially available crystalline celluloseis typically 60% or more.

In the cellulose-containing raw material, the cellulose content in theresidual component in the case of eliminating water from the rawmaterial is preferably 20% by mass or more, more preferably 40% by massor more, and still more preferably 60% by mass or more. For example, inthe commercially available pulp, the cellulose content in the residualcomponent in the case of eliminating water therefrom is typically 75 to99% by mass, and lignin and the like are contained as other component. Amethod for eliminating water from the raw material is not particularlylimited, and the water can be eliminated by, for example, vacuum dryingor drying with dry air. In this specification, the aforementionedcellulose content means a total amount of the cellulose amount and thehemicellulose amount. The cellulose content can be measured by themethod described in the section of Examples of JP 2011-137094 A.

In the case of using, as the cellulose-containing raw material, a pulp,a regenerated paper, or the like, from the viewpoint of improving theviscoelasticity of the asphalt composition, the lignin amount in thecellulose-containing raw material is preferably 20% by mass or less,more preferably 15% by mass or less, and still more preferably 10% bymass or less. A structural unit of the lignin is not particularlylimited, and there are exemplified known ones. From the viewpoint ofimproving the viscoelasticity of the asphalt composition, the structuralunit of the lignin is preferably a guaiacyl type, a syringyl type, or ap-hydroxyphenyl type.

Examples of a method for reducing the lignin include the alkalinecooking method described in JP 2008-92910 A; and the sulfuric aciddecomposition method described in JP 2005-229821 A.

The moisture content of the cellulose-containing raw material ispreferably 10% by mass or less, more preferably 5% by mass or less,still more preferably 3% by mass or less, and yet still more preferably1.8% by mass or less. When the moisture content of thecellulose-containing raw material is 10% by mass or less, not only thecellulose-containing raw material can be easily pulverized, but also thedecrystallization rate by the pulverization treatment is improved,whereby the crystallization index can be efficiently lowered for a shorttime.

The cellulose-containing raw material that is used for thedecrystallization treatment in the present invention is preferably onehaving a bulk density preferably ranging from 50 to 600 kg/m³ and aspecific surface area preferably ranging from 0.2 to 750 m²/kg.

From the viewpoint of more efficiently performing the pulverization andthe decrystallization, the bulk density of the cellulose-containing rawmaterial that is used for the decrystallization treatment in the presentinvention is preferably 50 kg/m³ or more, more preferably 65 kg/m³ ormore, and still more preferably 100 kg/m³ or more. When this bulkdensity is 50 kg/m³ or more, the cellulose-containing raw material hasan appropriate capacity, and therefore, handling properties areimproved. In addition, the amount of the raw material charged in apulverizer can be made high, and therefore, the processing capability isimproved. Meanwhile, from the viewpoint of handling properties andproductivity, an upper limit of this bulk density is preferably 600kg/m³ or less, more preferably 500 kg/m³ or less, and still morepreferably 400 kg/m³ or less. From these viewpoints, the bulk density ispreferably 50 to 600 kg/m³, more preferably 65 to 500 kg/m³, and stillmore preferably 100 to 400 kg/m³. The bulk density can be measured bythe method described in the section of Examples of JP 2011-1547 A.

From the viewpoint of efficiently dispersing the pulverized raw materialin a pulverizer, the cellulose-containing raw material to be supplied inthe pulverizer is preferably one having a specific surface area in arange of 0.2 m²/kg or more and 750 m²/kg or less. When this specificsurface area is 0.2 m²/kg or more, when supplying in the pulverizer, thepulverized raw material can be efficiently dispersed in the pulverizer,and it can attain the predetermined crystallization index and particlediameter without requiring a long time. Meanwhile, from the viewpoint ofproductivity, an upper limit of this specific surface area is preferably750 m²/kg or less. From these viewpoints, this specific surface area ismore preferably 0.65 m²/kg or more, and still more preferably 0.8 m²/kgor more, and it is more preferably 200 m²/kg or less, and still morepreferably 50 m²/kg or less. The specific surface area can be measuredby the method described in the section of Examples of JP 2011-1547 A.

By treating the cellulose-containing raw material with a pulverizer, thecellulose-containing raw material is pulverized, whereby the cellulosecan be efficiently decrystallized for a short time.

In the case where the cellulose-containing raw material to be suppliedin the pulverizer is in a chip form of 1 mm in square or more, from theviewpoint of efficiently dispersing the pulverized raw material in thepulverizer, the specific surface area is preferably 0.2 m²/kg or more,more preferably 0.65 m²/kg or more, and still more preferably 0.8 m²/kgor more, and it is preferably 4 m²/kg or less, more preferably 3.5 m²/kgor less, and still more preferably 3 m²/kg or less.

In the case where the cellulose-containing raw material to be suppliedin the pulverizer is in a particulate form of 1 mm or less, from theviewpoint of productivity and efficiently dispersing the pulverized rawmaterial in the pulverizer, the specific surface area is preferably 3m²/kg or more, more preferably 4.5 m²/kg or more, and still morepreferably 7.5 m²/kg or more, and it is preferably 750 m²/kg or less,more preferably 200 m²/kg or less, and still more preferably 50 m²/kg orless.

[Pre-Treatment of Decrystallization Treatment]

In the case of using a cellulose-containing raw material having a bulkdensity of less than 50 kg/m³, it is preferred to perform apre-treatment so as to have a bulk density in a range of 50 kg/m³ ormore and 600 kg/m³ or less, or a specific surface area in a range of 0.2m²/kg or more and 750 m²/kg or less. For example, by performing acutting treatment and/or a coarse pulverization treatment as thepre-treatment of the cellulose-containing raw material, it is possibleto control the bulk density and the specific surface area of thecellulose-containing raw material to the aforementioned preferredranges. From the viewpoint of producing the amorphous cellulose in asmall number of processes, it is preferred to perform the cuttingtreatment as the pre-treatment of the cellulose-containing raw material.

[Cutting Treatment]

As a method for cutting the cellulose-containing raw material, anappropriate method can be selected according to the type and shape ofthe cellulose-containing raw material. Examples thereof include a methodof using at least one cutting machine selected from a shredder, aslitter cutter, and a rotary cutter.

In the case of using a sheet-form cellulose-containing raw material, ashredder or a slitter cutter is preferably used as the cutting machine,and from the viewpoint of productivity, a slitter cutter is morepreferably used.

When a slitter cutter is used, the sheet-form cellulose-containing rawmaterial is cut along the longitudinal direction thereof by means of aroller cutter, thereby providing long strips. Subsequently, the longstrips are cut into short pieces along the transverse (width) directionby means of fixed blades and rotary blades, thereby readily providingdice-form cellulose-containing raw material pieces. As the slittercutter, a sheet pelletizer, manufactured by HORAI Co., Ltd. or a supercutter, manufactured by Ogino Seiki Co., Ltd. can be preferably adopted.By means of this machine, a sheet-form cellulose-containing raw materialcan be cut into pieces of about 1 to 20 mm in square.

In the case where a wood material, such as lumber from thinning,pruned-off branch, and building waste, or a non-sheetcellulose-containing raw material is cut, a rotary cutter is preferablyused. A rotary cutter is configured of rotary blades and a screen. Bythe action of the rotary blades, cut pieces of the cellulose-containingraw material having a size equal to or smaller than the opening size ofthe screen can be readily provided. If required, a fixed blade isprovided, and the raw material can be cut by means of the rotary bladesand the fixed blade.

In the case of using a rotary cutter, the size of the resulting coarselypulverized product can be controlled by changing the opening size of thescreen. The opening size of the screen is preferably 1 to 70 mm, morepreferably 2 to 50 mm, and still more preferably 3 to 40 mm. When thescreen has an opening size of 1 mm or more, a coarsely pulverizedproduct having an appropriate bulkiness is obtained, and the handlingproperties thereof are improved. When the screen has an opening size of70 mm or less, the product has a size suitable as the pulverized rawmaterial to be subjected to a post-pulverization treatment, andtherefore, the load can be reduced.

The size of the cellulose-containing raw material obtained after thecutting treatment is preferably 1 mm in square or more, and morepreferably 2 mm in square or more, and it is preferably 70 mm in squareor less, and more preferably 50 mm in square or less. By cutting in theaforementioned size, a post-drying treatment can be efficientlyperformed with ease, and the load required for pulverization in thepost-pulverization treatment can be reduced.

[Coarse Pulverization Treatment]

Subsequently, the cellulose-containing raw material, preferably thecellulose-containing raw material obtained through the aforementionedcutting treatment, may be further subjected to a coarse pulverizationtreatment, as the need arises. The coarse pulverization treatment ispreferably an extrusion treatment. A compression shear force is allowedto act through an extruder treatment, thereby breaking the crystalstructure of cellulose. Thus, the cellulose-containing raw material ispowdered, whereby the bulk density can be further increased.

In the method of mechanically pulverizing the cellulose-containing rawmaterial by allowing a compression shear force to act, when animpact-type pulverizer that is conventionally generally adopted, forexample, a cutter mill, a hammer mill, and a pin mill, is adopted, thepulverized material tends to suffer from flocculation to become bulky,whereby the handling properties are deteriorated, and a mass-basedcapability is lowered. On the other hand, by using an extruder, apulverized raw material having a desired bulk density is obtained,resulting in improved handling properties.

Although the type of the extruder may be either a single-screw type or atwin-screw type, from the viewpoint of enhancement in conveyingcapability, etc., a twin-screw extruder is preferred.

As the twin-screw extruder, there can be used a conventionally knowntwin-screw extruder in which two screws are rotatably inserted into acylinder. The rotational directions of the two screws in the twin-screwextruder may be either identical or reverse to each other. From theviewpoint of enhancement in conveying capability, the screws arepreferably rotated in the same direction.

The type of meshing of the screws in the extruder may be any of acomplete meshing type, a partially meshing type, and a de-meshing type.From the viewpoint of enhancement in treating capability, an extruder ofa complete meshing type or a partially meshing type is preferred.

From the viewpoint of applying a strong compression shear force, theextruder is preferably provided with a so-called kneading disk segmentin any portion of the respective screws thereof.

The kneading disk segment is configured of a plurality of kneading diskswhich are continuously arranged in combination while offsetting theirpositions at a constant phase, for example, at intervals of 90°, and iscapable of applying an extremely strong shear force to thecellulose-containing raw material with rotation of the screws byforcibly passing the raw material through a narrow gap between thekneading disks or between the kneading disk and the cylinder. The screwpreferably has such a configuration that the kneading disk segments andthe screw segments are arranged in an alternate relation to each other.In the twin-screw extruder, the two screws are preferably identical instructure to each other.

As the method of the coarse pulverization treatment, a method in whichthe cellulose-containing raw material, preferably thecellulose-containing raw material obtained through the aforementionedcutting treatment, is charged into an extruder and continuously treated.A shear rate is preferably 10 sec⁻¹ or more, more preferably 20 sec⁻¹ ormore, still more preferably 50 sec⁻¹ or more, and yet still morepreferably 500 sec⁻¹ or more, and it is preferably 30,000 sec⁻¹ or less,and more preferably 3,000 sec⁻¹ or less. When the shear rate is 10 sec⁻¹or more, the pulverization effectively proceeds. Although othertreatment conditions are not particularly limited, a treatmenttemperature is preferably 5 to 200° C.

The number of passes by the extruder may be only one (pass) to attain asufficient effect. However, from the viewpoint of reducing thecrystallization index and polymerization degree of cellulose, in thecase where the one-pass treatment is unsatisfactory, 2 or more passesare preferably conducted. In addition, from the viewpoint ofproductivity, the number of passes is preferably 1 or more and 10 orless. By repeating the pass, coarse particles are pulverized, whereby apowdery cellulose-containing raw material having a less fluctuation inparticle diameter can be obtained. When conducting 2 or more passes, aplurality of the extruders may be arranged in series in consideration ofproduction capability.

From the viewpoint of efficiently dispersing the pulverized raw materialin the pulverizer for the decrystallization treatment, an averageparticle diameter (median diameter) of the cellulose-containing rawmaterial obtained after the coarse pulverization treatment is preferably0.01 mm or more and 1 mm or less. When this average particle diameter is1 mm or less, the pulverized raw material can be efficiently dispersedin the pulverizer in the decrystallization treatment, whereby theparticle diameter can be adjusted to a predetermined level withoutrequiring a long time. On the other hand, from the viewpoint ofproductivity, a lower limit of the average particle diameter ispreferably 0.01 mm or more. From these viewpoints, the average particlediameter is more preferably 0.03 mm or more, and sill more preferably0.05 mm or more, and it is more preferably 0.7 mm or less, and stillmore preferably 0.5 mm or less. The average particle diameter can bemeasured by the method described in the section of Examples.

[Drying Treatment]

In the present invention, it is preferred that the cellulose-containingraw material, preferably the cellulose-containing raw material obtainedthrough the aforementioned cutting treatment and/or coarse pulverizationtreatment, is subjected to a drying treatment before thedecrystallization treatment.

In general, cellulose-containing raw materials which are generallyusable, such as commercially available pulp, and biomass resources,e.g., paper, wood, plant stem, leaf, and husk, contains moisture in anamount exceeding 5% by mass, typically about 5 to 30% by mass.

In consequence, in the present invention, it is preferred to adjust themoisture content of the cellulose-containing raw material to 10% by massor less through a drying treatment.

The drying method may be appropriately selected from known drying means.Examples thereof include a hot air heating drying method, a conductionheating drying method, a dehumidified air drying method, a chilled airdrying method, a microwave drying method, an infrared drying method, asun drying method, a vacuum drying method, and a freeze drying method.

In the aforementioned drying methods, a known dryer can be appropriatelyselected and used. Examples thereof include a dryer described in“Outline of Particle Technology” (edited by The Association of PowderProcess Industry and Engineering, JAPAN, published by The InformationCenter of Particle Technology, Japan (1995), page 176).

These drying methods or dryers may be employed alone or in combinationof two or more thereof. Although any of a batch treatment and acontinuous treatment may be adopted for the drying treatment, from theviewpoint of productivity, a continuous drying is preferred.

From the viewpoint of thermal conduction efficiency, the continuousdryer is preferably a horizontal agitation dryer of a conduction heatingtype. Furthermore, from the viewpoint of preventing micro-dust andattaining stability of continuous discharge, a twin-screw horizontalagitation dryer is preferred. As the twin-screw horizontal agitationdryer, a twin-screw paddle dryer, manufactured by Nara Machinery Co.,Ltd. can be preferably used.

Although a temperature in the drying treatment cannot be unequivocallydetermined depending upon the drying means, drying time, etc., it ispreferably 10° C. or higher, more preferably 25° C. or higher, and stillmore preferably 50° C. or higher, and it is preferably 250° C. or lower,more preferably 180° C. or lower, and still more preferably 150° C. orlower. A treatment time is preferably 0.01 hour or more, and morepreferably 0.02 hours or more, and it is preferably 2 hours or less, andmore preferably 1 hour or less. If desired, the drying treatment may beperformed under reduced pressure. The pressure is preferably 1 kPa ormore, and more preferably 50 kPa or more, and it is preferably 120 kPaor less, and more preferably 105 kPa or less.

[Decrystallization Treatment]

A medium-type pulverizer can be preferably used as the pulverizer thatis used for the decrystallization treatment. The medium-type pulverizeris classified into a container driving-type pulverizer and a mediumagitating-type pulverizer.

Examples of the container driving-type pulverizer include a tumblingmill, a vibration mill, a planetary mill, and a centrifugal fluid mill.Of these, a vibration mill is preferred from the viewpoint of highpulverization efficiency and productivity.

Examples of the medium agitating-type pulverizer include a tower-typepulverizer, such as a tower mill; an agitation tank-type pulverizer,such as an Attritor, an Aquamizer, and a Sand grinder; a flow tank-typepulverizer, such as a Visco mill and a Pearl mill; a flow tube-typepulverizer; an annular-type pulverizer, such as a co-ball mill; and acontinuous-type dynamic pulverizer. Of these, an agitation tank-typepulverizer is preferred from the viewpoint of high pulverizationefficiency and productivity. In the case of using a mediumagitating-type pulverizer, a peripheral speed of the tip of agitationblades thereof is preferably 0.5 m/s or more, and more preferably 1 m/sor more, and it is preferably 20 m/s or less, and more preferably 15 m/sor less.

As for the type of the pulverizer, “Progress of Chemical Engineering,30th Collection, Control of Microparticle”, Institute of ChemicalEngineering, Tokai Division, Oct. 10, 1996, Maki-Shoten) can be made byreference.

Although the treatment method may be either a batch method or acontinuous method, from the viewpoint of productivity, a continuousmethod is preferred.

Examples of the medium include a ball, a rod, and a tube. Of these, fromthe viewpoint of high pulverization efficiency and productivity, a balland a rod are preferred, with a rod being more preferred.

The material of the medium of the pulverizer is not particularlylimited, and examples thereof include iron, stainless steel, alumina,zirconia, silicon carbide, silicon nitride, and glass.

In the case where the pulverizer is a vibration mill, and the medium isa ball, an outer diameter of the ball is preferably 0.1 mm or more, andmore preferably 0.5 mm or more, and it is preferably 100 mm or less, andmore preferably 50 mm or less. When the size of the ball falls withinthe aforementioned range, not only a desired pulverization force isattained, but also the cellulose can be efficiently decrystallizedwithout contamination of the cellulose-containing raw material to becaused due to inclusion of a fragment of the ball or the like.

In the present invention, cellulose in the raw material can beefficiently decrystallized through a pulverization treatment with avibration mill having a rod filled therein, and hence, such is suitable.

Examples of the vibration mill include a Vibro mill, manufactured byUras Techno Co., Ltd.; a vibration mill, manufactured by Chuo KakohkiCo., Ltd.; a small-size vibration rod mill “model 1045”, manufactured byYoshida Seisakusho Co., Ltd.; a vibration cup mill “model P-9”,manufactured by Fritsch Inc., in Germany; and a small-size vibrationmill “model NB-O”, manufactured by Nitto Kagaku Co., Ltd.

The rod that is used as the medium in the pulverizer is a rod-formmedium, and rods having a cross section, such as a polygonal shape,e.g., a square shape and a hexagonal shape, a circular shape, and anelliptical shape, can be used.

An outer diameter of the rod is preferably 0.5 mm or more, morepreferably 1 mm or more, and still more preferably 5 mm or more, and itis preferably 200 mm or less, more preferably 100 mm or less, and stillmore preferably 50 mm or less. A length of the rod is not particularlylimited so long as it is shorter than the length of the container of thepulverizer. When the size of the rod falls within the aforementionedrange, not only a desired pulverization force is obtained, but also thecellulose can be efficiently decrystallized without contamination of thecellulose-containing raw material to be caused due to inclusion of afragment of the rod or the like.

Although a filling ratio of the medium, such as a ball and a rod, variesin terms of a suitable range thereof depending upon the type of thepulverizer, it is preferably 10% or more, and more preferably 15% ormore, and it is preferably 97% or less, and more preferably 95% or less.When the filling ratio falls within the aforementioned range, not onlythe frequency of contact between the cellulose-containing raw materialand the medium can be increased, but also the pulverization efficiencycan be improved without inhibiting the motion of the medium. The“filling ratio” as referred to herein means an apparent volume of themedium relative to a capacity of the agitation section of thepulverizer.

Although a treatment time of the pulverizer cannot be unequivocallydetermined and varies depending upon the type of the pulverizer, thetype, size, filling ratio, etc. of the medium, such as a ball and a rod,from the viewpoint of reducing the crystallization index, it ispreferably 0.5 minutes or more, more preferably 2 minutes or more, sillmore preferably 3 minutes or more, yet still more preferably 4 minutesor more, and even yet still more preferably 5 minutes or more, and it ispreferably 24 hours or less, more preferably 12 hours or less, stillmore preferably 6 hours or less, yet still more preferably 1 hour orless, and even yet still more preferably 40 minutes or less.

Although a treatment temperature is not particularly limited, from theviewpoint of preventing the deterioration of cellulose to be caused dueto heat, it is preferably 5° C. or higher, and more preferably 10° C. orhigher, and it is preferably 250° C. or lower, and more preferably 200°C. or lower.

[Particle Diameter Reduction Treatment]

In the present invention, if desired, the amorphous cellulose obtainedthrough the decrystallization treatment may be further subjected to aparticle diameter reduction treatment. The particle diameter reductiontreatment can be performed by appropriately selecting and using a knownpulverizer, and examples of the pulverizer include those described in“Handbook of Chemical Engineering, revised 6th edition” (edited by TheSociety of Chemical Engineers, Japan, published by Maruzen Co., Ltd.(1999), page 843).

These pulverizers may be used alone or in combination of two or morethereof. Although the particle diameter reduction treatment may beeither a batch method or a continuous method, a continuous method ispreferred from the viewpoint of productivity.

From the viewpoint of high pulverization efficiency and reduction of theparticle diameter, the pulverizer is preferably a high-speed rotarymill, and more preferably a turbo-type mill and an annular-type mill. Asthe turbo-type mill, a turbo mill, manufactured by Turbo Corporation canbe preferably used. As the annular-type mill, Kryptron Series,manufactured by EARTHTECHNICA Co., Ltd. can be preferably used.

As the method of particle diameter treatment, a method in which theamorphous cellulose obtained through the decrystallization treatment ischarged in the pulverizer and continuously processed is preferred. Fromthe viewpoint of obtaining the amorphous cellulose having a smallparticle diameter, a peripheral speed of the high-speed rotary mill ispreferably 50 m/s or more, and more preferably 100 m/s or more. Althoughother treatment conditions are not particularly limited, a treatmenttemperature is preferably 5° C. or higher and 200° C. or lower.

[Classification Treatment]

In the present invention, if desired, the amorphous cellulose obtainedthrough the decrystallization treatment can be further subjected to aclassification treatment. Amorphous cellulose having a desired particlediameter can be obtained through the treatment with classifier. Theclassification treatment method may be performed through a techniqueappropriately selected from known dry classification means, and examplesthereof include sieving and pneumatic classification.

By again charging a coarse powder after the classification treatmenttogether with the cellulose-containing raw material in the vibrationmill, amorphous cellulose having a small particle diameter can beefficiently obtained.

Thus, cellulose (amorphous cellulose) having a crystallization index of50% or less is obtained.

Although the thus obtained cellulose is decrystallized to an extent thatthe crystallization index is 50% or less, from the viewpoint ofimprovement in viscoelasticity of the asphalt composition and theviewpoint of handling properties, the median diameter (volume medialparticle diameter) is preferably 200 μm or less, more preferably 150 μmor less, still more preferably 100 μm or less, and yet still morepreferably 80 μm or less, and it is preferably 1 μm or more, morepreferably 3 μm or more, still more preferably 5 μm or more, and yetstill more preferably 10 μm or more.

In the case where the amorphous cellulose is cellulose subjected to asurface hydrophobization treatment as mentioned later, the mediandiameter of the cellulose means a median diameter of the amorphouscellulose after the surface hydrophobization treatment, and a preferredrange thereof is the same.

In the present invention, the amorphous cellulose is preferably asurface-hydrophobized cellulose. Although a hydrophobizing agent forperforming the surface hydrophobization treatment is not particularlylimited, it is preferably at least one selected from a silane-basedcoupling agent, a titanate-based coupling agent, an aluminum-basedcoupling agent, a silicon oil, a fluorine oil, a silicon resin, afluorine resin, an acrylic resin, and a polymer having a polar group anda polyolefin chain.

Examples of the silane-based coupling agent include trimethylmethoxysilane, dimethyl methoxysilane, methyl trimethoxysilane, methyltriethoxysilane, vinyl trimethoxysilane, γ-aminopropyl triethoxysilane,and fluoromethyl trimethoxysilane.

Examples of the titanate-based coupling agent include isopropyltriisostearoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate,isopropyl tris(N-aminoethyl-aminoethyl) titanate, and bis(dioctylpyrophosphate) ethylene titanate.

Examples of the aluminum-based coupling agent include ethyl acetoacetatealuminum diisopropylate, aluminum tris(ethyl acetoacetate), an alkylacetoacetate aluminum diisopropylate, aluminum monoacetyl acetatebis(ethyl acetoacetate), and aluminum tris(acetyl acetate).

As the polymer having a polar group and a polyolefin chain, the polymershaving a polar group and a polyolefin chain, which are exemplified asthe modifier in the polymer-modified asphalt, are exemplified, and apreferred range thereof is also the same.

Of these, the surface hydrophobizing agent is preferably at least oneselected from a silane-based coupling agent, a titanate-based couplingagent, an aluminum-based coupling agent, and a polymer having a polargroup and a polyolefin chain; more preferably a polymer having a polargroup and a polyolefin chain; still more preferably a maleicanhydride-modified polyolefin; yet still more preferably at least oneselected from maleic anhydride-modified polyethylene and maleicanhydride-modified polypropylene; even yet still more preferably maleicanhydride-modified polyethylene or maleic anhydride-modifiedpolypropylene; and even still more preferably maleic anhydride-modifiedpolypropylene.

From the viewpoint of improving the viscoelasticity of the asphaltcomposition, the treatment amount with the surface hydrophobizing agentis preferably 1 part by mass or more, more preferably 3 parts by mass ormore, still more preferably 5 parts by mass or more, yet still morepreferably 10 parts by mass or more, and even yet still more preferably20 parts by mass or more, and it is preferably 100 parts by mass orless, more preferably 80 parts by mass or less, still more preferably 60parts by mass or less, yet still more preferably 40 parts by mass orless, and even yet still more preferably 30 parts by mass or less, basedon 100 parts by mass of the untreated amorphous cellulose.

Although the surface hydrophobization treatment method of the amorphouscellulose is not particularly limited, it is preferably a method inwhich the surface hydrophobizing agent is added together with thecellulose in the pulverizer during the aforementioned decrystallizationtreatment, thereby mixing and pulverizing the contents. That is, it ispreferred to produce the surface-hydrophobized cellulose by adding thesurface hydrophobizing agent to cellulose having a crystallization indexof more than 50%, followed by mixing and pulverizing, therebycontrolling the crystallization index to 50% or less.

The surface hydrophobization treatment method is not limited thereto,and the surface treatment may be performed by agitating and mixing thecellulose together with the surface hydrophobizing agent in awater-soluble organic solvent. Examples of the water-soluble organicsolvent include methyl alcohol, ethyl alcohol, propyl alcohol, isopropylalcohol, and acetone.

In the asphalt composition of the present invention, the content of theamorphous cellulose is 0.01 part by mass or more and 10 parts by mass orless based on 100 parts by mass of the asphalt. When the content of theamorphous cellulose is 0.01 part by mass or more, an improving effectfor rutting or cracking is high. On the other hand, when the content ofthe amorphous cellulose is 10 parts by mass or less, such is preferredfrom the viewpoint of costs. The improvement for rutting or crackingmeans inhibition of the occurrence of rutting or cracking. Hereunder,the same is applicable.

The content of the amorphous cellulose is preferably 0.03 parts by massor more, more preferably 0.1 part by mass or more, still more preferably0.3 parts by mass or more, yet still more preferably 1 part by mass ormore, and even yet still more preferably 2 parts by mass or more, and itis preferably 8 parts by mass or less, more preferably 6 parts by massor less, and still more preferably 4 parts by mass or less, based on 100parts by mass of the asphalt.

In the case where the asphalt is a polymer-modified asphalt, the mass ofthe asphalt means a mass of the whole of asphalt including the straightasphalt and the modifier.

Similarly, in the case where the amorphous cellulose is asurface-hydrophobized cellulose, the mass of the amorphous cellulosemeans a mass of the whole of amorphous cellulose include the cellulosemain body and the surface hydrophobizing agent.

From the viewpoint of improving rutting or cracking, the content of theamorphous cellulose in the asphalt composition of the present inventionis preferably 0.01% by mass or more, more preferably 0.03% by mass ormore, still more preferably 0.1% by mass or more, yet still morepreferably 0.3% by mass or more, even yet still more preferably 1% bymass or more, and even still more preferably 2% by mass or more; andfrom the viewpoint of costs, it is preferably 10% by mass or less, morepreferably 8% by mass or less, still more preferably 6% by mass or less,and yet still more preferably 4% by mass or less.

From the viewpoint of exhibiting an asphalt performance, the content ofthe asphalt in the asphalt composition of the present invention ispreferably 50% by mass or more, more preferably 70% by mass or more,still more preferably 90% by mass or more, yet still more preferably 92%by mass or more, even yet still more preferably 94% by mass or more, andeven still more preferably 96% by mass or more; and from the viewpointof containing the amorphous cellulose and improving the rutting orcracking, it is preferably 99.99% by mass or less, more preferably99.97% by mass or less, still more preferably 99.9% by mass or less, yetstill more preferably 99.7% by mass or less, even yet still morepreferably 99% by mass or less, and even still more preferably 98% bymass or less.

To the asphalt composition of the present invention, in addition to theaforementioned asphalt and amorphous cellulose, various additives whichare conventionally commonly used for asphalt compositions, such as afilm-forming agent, a thickening stabilizer, and an emulsifier, may beadded, as the need arises.

Specifically, examples thereof include fillers and reinforcing agents,such as calcium carbonate, a mineral substance powder, and a glassfiber; aggregates of a mineral substance; pigments, such as red ironoxide and titanium dioxide; waxes, such as a paraffin wax, amicrocrystalline wax, and a low-molecular weight polyethylene wax;foaming agents, such as azodicarbonamide; polyolefin-based orlow-molecular weight vinyl aromatic thermoplastic resins, such asatactic polypropylene and an ethylene-ethyl acrylate copolymer; naturalrubbers; and synthetic rubbers, such as a polyisoprene rubber, apolybutadiene rubber, a styrene-butadiene rubber, an ethylene-propylenerubber, a chloroprene rubber, an acrylic rubber, an isoprene-isobutylenerubber, a polypentenamer rubber, a styrene-butadiene-based blockcopolymer, a styrene-isoprene-based block copolymer, a hydrogenatedstyrene-butadiene-based block copolymer, and a hydrogenatedstyrene-isoprene-based block copolymer.

The total addition amount of these additives is preferably 50% by massor less, more preferably 30% by mass or less, still more preferably 20%by mass or less, yet still more preferably 10% by mass or less, and evenyet still more preferably 5% by mass or less relative to the whole ofthe asphalt composition.

[Production Method of Asphalt Composition]

A production method of the asphalt composition of the present inventionincludes a step of mixing asphalt and amorphous cellulose.

The asphalt composition is obtained by heat-melting asphalt, addingamorphous cellulose and optionally other additive, and agitating andmixing the contents in a generally used mixing machine until therespective components are uniformly dispersed.

Examples of the generally used mixing machine include a homomixer, adissolver, a puddle mixer, a ribbon mixer, a screw mixer, a planetarymixer, a vacuum counter-flow mixer, a roll mill, and a twin-screwextruder.

From the viewpoint of uniformly dispersing the amorphous cellulose inthe asphalt, a mixing temperature of the aforementioned asphalt andamorphous cellulose is preferably 100° C. or higher, more preferably130° C. or higher, still more preferably 160° C. or higher, and yetstill more preferably 170° C. or higher, and it is preferably 230° C. orlower, more preferably 210° C. or lower, still more preferably 200° C.or lower, and yet still more preferably 190° C. or lower.

From the viewpoint of efficiently uniformly dispersing the amorphouscellulose in the asphalt, a mixing time of the asphalt and the amorphouscellulose is preferably 0.1 hour or more, more preferably 0.5 hours ormore, still more preferably 1.0 hour or more, and yet still morepreferably 1.5 hours or more, and it is preferably 10 hours or less,more preferably 7 hours or less, still more preferably 5 hours or less,and yet still more preferably 3 hours or less.

The preferred content of the amorphous cellulose relative to the asphaltis one as mentioned above.

As mentioned above, the amorphous cellulose that is used for the asphaltcomposition of the present invention and the production method of thesame is amorphous cellulose having a crystallization index of 50% orless, and preferably a surface-hydrophobized cellulose.

It is preferred that the surface-hydrophobized cellulose is producedthrough a step of adding a surface hydrophobizing agent to cellulosehaving a crystallization index of more than 50%, followed by mixing andpulverizing, thereby controlling the crystallization index to 50% orless.

[Additive for Asphalt]

An additive for asphalt of the present invention includes cellulosehaving a crystallization index of 50% or less. The cellulose (amorphouscellulose) having a crystallization index of 50% or less is one obtainedby the aforementioned method, and it is preferably asurface-hydrophobized cellulose.

The additive for asphalt is used upon being mixed with asphalt, and theaddition amount of the additive for asphalt is preferably 0.01 part bymass or more and 10 parts by mass or less based on 100 parts by mass ofthe asphalt. When the addition amount of the additive for asphalt isless than 0.01 part by mass, the improving effect for rutting orcracking is low. On the other hand, when the content of the additive forasphalt is more than 10 parts by mass, such is not preferred from theviewpoint of costs.

The addition amount of the additive for asphalt is more preferably 0.03parts by mass or more, still more preferably 0.1 part by mass or more,yet still more preferably 0.3 parts by mass or more, even yet still morepreferably 1 part by mass or more, and even still more preferably 2parts by mass or more, and it is more preferably 8 parts by mass orless, still more preferably 6 parts by mass or less, and yet still morepreferably 4 parts by mass or less, based on 100 parts by mass ofasphalt.

In the case where the asphalt is a polymer-modified asphalt, the mass ofthe asphalt means a mass of the whole of asphalt including the straightasphalt and the modifier.

Similarly, in the case where the additive for asphalt is asurface-hydrophobized cellulose, the mass of the additive for asphaltmeans a mass as the whole including the cellulose main body and thesurface hydrophobizing agent.

[Asphalt Mixture and Production Method of Same]

The asphalt composition of the present invention is a binder compositionand is used for pavement after adding an aggregate thereto to provide anasphalt mixture. That is, the asphalt composition of the presentinvention is suitable for pavement, and especially suitable for roadpavement.

The aggregate can be, for example, optionally selected from crushedstone, cobble stone, gravel, sand, reclaimed aggregate, and ceramics,and used.

As the aggregate, all of a coarse aggregate having a particle diameterof 2.36 mm or more and a fine aggregate having a particle diameter ofless than 2.36 mm can be used. Examples of the coarse aggregate includeNo. 7 crushed stone having a particle diameter range of 2.36 mm or moreand less than 4.75 mm, No. 6 crushed stone having a particle diameterrange of 4.75 mm or more and less than 13.2 mm, No. 5 crushed stonehaving a particle diameter range of 13.2 mm or more and less than 19 mm,and No. 4 crushed stone having a particle diameter range of 19 mm ormore and less than 31.5 mm.

The fine aggregate is preferably a fine aggregate having a particlediameter of 0.075 mm or more and less than 2.36 mm.

Examples of the fine aggregate include river sand, hill sand, mountainsand, sea sand, crushed sand, fine sand, screenings, crushed stone dust,silica sand, artificial sand, glass cullet, molding sand, and reclaimedaggregate-crushed sand.

The aforementioned particle diameter is a value prescribed in JIS5001-1995.

Of these, a combination of the coarse aggregate and the fine aggregateis preferred.

The fine aggregate may contain a filler having a particle diameter ofless than 0.075 mm (for example, sand). A lower limit value of theaverage particle diameter of the filler is, for example, 0.001 mm ormore.

From the viewpoint of improving the dry strength, the average particlediameter of the filler is preferably 0.001 mm or more, and from the sameviewpoint, it is preferably 0.05 mm or less, more preferably 0.03 mm orless, and still more preferably 0.02 mm or less. The average particlediameter of the filler can be measured by a laser diffraction particlesize distribution analyzer. Here, the average particle diameter means anaverage particle diameter of 50% cumulative volume.

[Measurement Method of Average Particle Diameter of Filler]

The average particle diameter of the filler is a value measured by alaser diffraction particle size distribution analyzer (“LA-950”,manufactured by HORIBA, Ltd.) with the following conditions.

Measurement method: Flow method

Dispersion medium: Ethanol

Sample preparation: 2 mg/100 mL

Dispersing method: Stirring and 1 minute of built-in ultrasonic waves

Examples of the filler include sand, fly ash, calcium carbonate, andhydrated lime. Of these, calcium carbonate is preferred from theviewpoint of improving the dry strength.

A mass ratio of the coarse aggregate to the fine aggregate is preferably10/90 or more, more preferably 20/80 or more, and still more preferably30/70 or more, and it is preferably 90/10 or less, more preferably 80/20or less, and still more preferably 70/30 or less.

The content of the aggregate is preferably 1,000 parts by mass or more,more preferably 1,200 parts by mass or more, and still more preferably1,500 parts by mass or more, and it is preferably 3,000 parts by mass orless, more preferably 2,500 parts by mass or less, and still morepreferably 2,000 parts by mass or less, based on 100 parts by mass ofthe asphalt composition.

The blending ratio of asphalt in the conventional asphalt mixturescontaining the aggregate and the asphalt may be in general determined byreferring to an optimum asphalt amount obtained from “Formulation andDesign of Asphalt Mixture” as described in “Guideline for PavementDesign and Construction” published by Japan Road Association.

In the present invention, the aforementioned optimum asphalt amountcorresponds to the total amount of the asphalt and the amorphouscellulose. In consequence, in general, the total blending amount of theasphalt and the amorphous cellulose is preferably determined from theaforementioned optimum asphalt amount.

However, it is not needed to limit the optimum asphalt amount to themethod as described in “Guideline for Pavement Design and Construction”,and it may also be determined by any other methods.

The asphalt mixture of the present invention may be used as a heatedasphalt mixture not substantially containing water, or may also be usedas a cold asphalt mixture obtained by blending the aforementionedasphalt mixture with an emulsifier or water to provide an asphaltemulsion, with which is then blended an aggregate or the like.

In particular, the asphalt composition of the present invention has suchproperties that the amorphous cellulose is apt to be uniformly dispersedin the asphalt composition. Therefore, when used as a heated asphaltmixture, it is able to effectively exhibit its characteristic features.

In the case of using the asphalt mixture as a heated asphalt mixture,the method for producing the asphalt mixture is not particularlylimited, and the asphalt mixture may be produced by any methods.However, in general, the asphalt mixture may be produced according toany method for producing an asphalt mixture containing an aggregate andan asphalt composition.

The method for producing the asphalt mixture of the present inventionpreferably includes a step of preparing an asphalt composition havingasphalt and amorphous cellulose and mixing an aggregate therewith at130° C. or higher and 200° C. or lower.

From the viewpoint of softening the asphalt, the mixing temperature ispreferably 140° C. or higher, and it is preferably 190° C. or lower, andmore preferably 180° C. or lower.

A mixing time is preferably 30 seconds or more, more preferably 1 minuteor more, still more preferably 2 minutes or more, and yet still morepreferably 5 minutes or more. Although an upper limit of the mixing timeis not particularly limited, it is, for example, about 30 minutes.

As the specific production method, it is preferred to add the amorphouscellulose to the asphalt composition in the step of mixing the aggregateand the asphalt composition in a production method of the asphaltmixture which is called as a conventional plant mix (premix) method. Inaddition, in producing the asphalt mixture, the aggregate, the asphalt,and the amorphous cellulose may be mixed.

[Road Paving Method]

The asphalt composition of the present invention is suitable for roadpavement, and as mentioned above, the asphalt mixture having theaggregate added to the asphalt composition is used for paving the road.

The road paving method of the present invention preferably includes astep of laying the asphalt mixture of the present invention on a road orthe like, thereby forming an asphalt paving material layer.

In the road paving method, the asphalt mixture may be subjected tocompacting laying using the same laying machines and the same layingmethod as used for ordinary asphalt mixtures. In the case of using theasphalt mixture as a heated asphalt mixture, a compacting temperature ofthe asphalt mixture is preferably 100° C. or higher, more preferably120° C. or higher, and still more preferably 130° C. or higher, and itis preferably 200° C. or lower, more preferably 180° C. or lower, andstill more preferably 170° C. or lower.

With respect to the aforementioned embodiments, the present inventionfurther discloses the following asphalt composition, method forproducing an asphalt composition, and additive for asphalt. <1> Anasphalt composition containing asphalt and cellulose, wherein thecontent of the cellulose is 0.01 part by mass or more and 10 parts bymass or less based on 100 parts by mass of the asphalt, and acrystallization index of the cellulose is 50% or less.

<2> The asphalt composition as set forth in <1>, wherein the asphalt isselected from a straight asphalt and a polymer-modified asphalt, andpreferably a polymer-modified asphalt.<3> The asphalt composition as set forth in <1> or <2>, wherein theasphalt is a polymer-modified asphalt containing a polymer having apolar group and a polyolefin chain.<4> The asphalt composition as set forth in <3>, wherein the polymerhaving a polar group and a polyolefin chain is preferably a maleicanhydride-modified polyolefin, more preferably at least one selectedfrom maleic anhydride-modified polypropylene and maleicanhydride-modified polyethylene, still more preferably maleicanhydride-modified polypropylene or maleic anhydride-modifiedpolyethylene, and yet still more preferably maleic anhydride-modifiedpolypropylene.<5> The asphalt composition as set forth in <4>, wherein a weightaverage molecular weight of the maleic anhydride-modified polyolefin,preferably maleic anhydride-modified polyethylene or maleicanhydride-modified polypropylene, is preferably 1,000 or more, morepreferably 5,000 or more, still more preferably 10,000 or more, and yetstill more preferably 30,000 or more.<6> The asphalt composition as set forth in <4> or <5>, wherein a weightaverage molecular weight of the maleic anhydride-modified polyolefin,preferably maleic anhydride-modified polyethylene or maleicanhydride-modified polypropylene, is preferably 1,000,000 or less, morepreferably 500,000 or less, still more preferably 300,000 or less, andyet still more preferably 100,000 or less.<7> The asphalt composition as set forth in any of <4> to <6>, wherein aweight average molecular weight of the maleic anhydride-modifiedpolyolefin, preferably maleic anhydride-modified polyethylene or maleicanhydride-modified polypropylene, is preferably 1,000 or more and1,000,000 or less, more preferably 5,000 or more and 500,000 or less,still more preferably 10,000 or more and 300,000 or less, and yet stillmore preferably 30,000 or more and 100,000 or less.<8> The asphalt composition as set forth in any of <3> to <7>, whereinthe asphalt is a polymer-modified asphalt containing a polymer(modifier) having a polar group and a polyolefin chain, and the amountof the modifier added to the straight asphalt is preferably 0.1 part bymass or more, more preferably 0.3 parts by mass or more, still morepreferably 0.5 parts by mass or more, and yet still more preferably 0.8parts by mass or more based on 100 parts by mass of the straightasphalt.<9> The asphalt composition as set forth in any of <3> to <8>, whereinthe asphalt is a polymer-modified asphalt containing a polymer(modifier) having a polar group and a polyolefin chain, and the amountof the modifier added to the straight asphalt is preferably 20 parts bymass or less, more preferably 10 parts by mass or less, still morepreferably 5 parts by mass or less, and yet still more preferably 2parts by mass or less based on 100 parts by mass of the straightasphalt.<10> The asphalt composition as set forth in any of <3> to <9>, whereinthe asphalt is a polymer-modified asphalt containing a polymer(modifier) having a polar group and a polyolefin chain, and the amountof the modifier added to the straight asphalt is preferably 0.1 part bymass or more and 20 parts by mass or less, more preferably 0.3 parts bymass or more and 10 parts by mass or less, still more preferably 0.5parts by mass or more and 5 parts by mass or less, and yet still morepreferably 0.8 parts by mass or more and 2 parts by mass or less basedon 100 parts by mass of the straight asphalt.<11> The asphalt composition as set forth in any of <1> to <10>, whereinthe crystallization index of the cellulose is preferably 45% or less,and more preferably 40% or less.<12> The asphalt composition as set forth in any of <1> to <11>, whereinthe crystallization index of the cellulose is preferably 1% or more, andmore preferably 10% or more.<13> The asphalt composition as set forth in any of <1> to <12>, whereinthe crystallization index of the cellulose is preferably 1% or more and45% or less, and more preferably 10% or more and 40% or less.<14> The asphalt composition as set forth in any of <1> to <13>, whereina moisture content of a cellulose-containing raw material for obtainingthe cellulose is preferably 10% by mass or less, more preferably 5% bymass or less, still more preferably 3% by mass or less, and yet stillmore preferably 1.8% by mass or less.<15> The asphalt composition as set forth in any of <1> to <14>, whereinthe cellulose is a surface-hydrophobized cellulose.<16> The asphalt composition as set forth in <15>, wherein thesurface-hydrophobized cellulose is cellulose subjected to a surfacetreatment with at least one surface hydrophobizing agent selected from asilane-based coupling agent, a titanate-based coupling agent, analuminum-based coupling agent, and a polymer having a polar group and apolyolefin chain; preferably cellulose subjected to a surface treatmentwith a polymer having a polar group and a polyolefin chain; morepreferably cellulose subjected to a surface treatment with a polymerhaving a polar group and a polyolefin chain; still more preferablycellulose subjected to a surface treatment with a maleicanhydride-modified polyolefin; yet still more preferably cellulosesubjected to a surface treatment with at least one selected from maleicanhydride-modified polypropylene and maleic anhydride-modifiedpolyethylene; even yet still more preferably cellulose subjected to asurface treatment with maleic anhydride-modified polypropylene or maleicanhydride-modified polyethylene; and even still more preferablycellulose subjected to a surface treatment with maleicanhydride-modified polypropylene.<17> The asphalt composition as set forth in <15> or <16>, wherein thetreatment amount with the surface hydrophobizing agent is preferably 1part by mass or more, more preferably 3 parts by mass or more, stillmore preferably 5 parts by mass or more, yet still more preferably 10parts by mass or more, and even yet still more preferably 20 parts bymass or more based on 100 parts by mass of the untreated cellulose.<18> The asphalt composition as set forth in any of <15> to <17>,wherein the treatment amount with the surface hydrophobizing agent ispreferably 100 parts by mass or less, more preferably 80 parts by massor less, still more preferably 60 parts by mass or less, yet still morepreferably 40 parts by mass or less, and even yet still more preferably30 parts by mass or less based on 100 parts by mass of the untreatedcellulose.<19> The asphalt composition as set forth in any of <15> to <18>,wherein the treatment amount with the surface hydrophobizing agent ispreferably 1 part by mass or more and 100 parts by mass or less, morepreferably 3 parts by mass or more and 80 parts by mass or less, stillmore preferably 5 parts by mass or more and 60 parts by mass or less,yet still more preferably 10 parts by mass or more and 40 parts by massor less, and even yet still more preferably 20 parts by mass or more and30 parts by mass or less based on 100 parts by mass of the untreatedcellulose.<20> The asphalt composition as set forth in any of <1> to <19>, whereinthe content of the cellulose is preferably 0.03 parts by mass or more,more preferably 0.1 part by mass or more, still more preferably 0.3parts by mass or more, yet still more preferably 1 part by mass or more,and even yet still more preferably 2 parts by mass or more based on 100parts by mass of the asphalt.<21> The asphalt composition as set forth in any of <1> to <20>, whereinthe content of the cellulose is preferably 8 parts by mass or less, morepreferably 6 parts by mass or less, and still more preferably 4 parts bymass or less based on 100 parts by mass of the asphalt.<22> The asphalt composition as set forth in any of <1> to <21>, whereinthe content of the cellulose is preferably 0.03 parts by mass or moreand 8 parts by mass or less, more preferably 0.1 part by mass or moreand 6 parts by mass or less, still more preferably 0.3 parts by mass ormore and 4 parts by mass or less, yet still more preferably 1 part bymass or more and 4 parts by mass or less, and even yet still morepreferably 2 parts by mass or more and 4 parts by mass or less based on100 parts by mass of the asphalt.<23> The asphalt composition as set forth in any of <1> to <22>, whereinthe content of the cellulose in the asphalt composition is preferably0.01% by mass or more, more preferably 0.03% by mass or more, still morepreferably 0.1% by mass or more, yet still more preferably 0.3% by massor more, even yet still more preferably 1% by mass or more, and evenstill more preferably 2% by mass or more.<24> The asphalt composition as set forth in any of <1> to <23>, whereinthe content of the cellulose in the asphalt composition is preferably10% by mass or less, more preferably 8% by mass or less, still morepreferably 6% by mass or less, and yet still more preferably 4% by massor less.<25> The asphalt composition as set forth in any of <1> to <24>, whereinthe content of the cellulose in the asphalt composition is preferably0.01% by mass or more and 10% by mass or less, more preferably 0.03% bymass or more and 8% by mass or less, still more preferably 0.1% by massor more and 6% by mass or less, yet still more preferably 0.3% by massor more and 4% by mass or less, even yet still more preferably 1% bymass or more and 4% by mass or less, and even still more preferably 2%by mass or more and 4% by mass or less.<26> The asphalt composition as set forth in any of <1> to <25>, whereinthe content of the asphalt in the asphalt composition is preferably 50%by mass or more, more preferably 70% by mass or more, still morepreferably 90% by mass or more, yet still more preferably 92% by mass ormore, even yet still more preferably 94% by mass or more, even stillmore preferably 96% by mass or more, and even still more furtherpreferably 98% by mass or more.<27> The asphalt composition as set forth in any of <1> to <26>, whereinthe content of the asphalt in the asphalt composition is preferably99.99% by mass or less, more preferably 99.97% by mass or less, stillmore preferably 99.9% by mass or less, yet still more preferably 99.7%by mass or less, even yet still more preferably 99% by mass or less, andeven still more preferably 98% by mass or less.<28> The asphalt composition as set forth in any of <1> to <27>, whereinthe content of the asphalt in the asphalt composition is preferably 50%by mass or more and 99.99% by mass or less, more preferably 70% by massor more and 99.97% by mass or less, still more preferably 90% by mass ormore and 99.9% by mass or less, yet still more preferably 92% by mass ormore and 99.7% by mass or less, even yet still more preferably 94% bymass or more and 99% by mass or less, and even still more preferably 96%by mass or more and 98% by mass or less.<29> The asphalt composition as set forth in any of <1> to <28>, whereina median diameter of the cellulose is preferably 200 μm or less, morepreferably 150 μm or less, still more preferably 100 μm or less, and yetstill more preferably 80 μm or less.<30> The asphalt composition as set forth in any of <1> to <29>, whereina median diameter of the cellulose is preferably 1 μm or more, morepreferably 3 μm or more, still more preferably 5 μm or more, and yetstill more preferably 10 μm or more.<31> The asphalt composition as set forth in any of <1> to <30>, whereina median diameter of the cellulose is preferably 1 μm or more and 200 μmor less, more preferably 3 μm or more and 150 μm or less, still morepreferably 5 μm or more and 100 μm or less, and yet still morepreferably 10 μm or more and 80 μm or less.<32> The asphalt composition as set forth in any of <1> to <31>, whichis to be used for road pavement.<33> The asphalt composition as set forth in any of <1> to <32>, whereinthe asphalt composition is a binder composition and is used for pavementafter adding an aggregate thereto to provide an asphalt mixture.<34> A method for producing the asphalt composition as set forth in anyof <1> to <33>, including a step of mixing asphalt and cellulose.<35> The method for producing the asphalt composition as set forth in<34>, wherein a mixing temperature of asphalt and cellulose ispreferably 100° C. or higher, more preferably 130° C. or higher, stillmore preferably 160° C. or higher, and yet still more preferably 170° C.or higher.<36> The method for producing the asphalt composition as set forth in<34> or<35>, wherein a mixing temperature of asphalt and cellulose ispreferably 230° C. or lower, more preferably 210° C. or lower, stillmore preferably 200° C. or lower, and yet still more preferably 190° C.or lower.<37> The method for producing the asphalt composition as set forth inany of <34> to <36>, wherein a mixing temperature of asphalt andcellulose is preferably 100° C. or higher and 230° C. or lower, morepreferably 130° C. or higher and 210° C. or lower, still more preferably160° C. or higher and 200° C. or lower, and yet still more preferably170° C. or higher and 190° C. or lower.<38> The method for producing the asphalt composition as set forth inany of <34> to <37>, wherein a mixing time of asphalt and cellulose ispreferably 0.1 hour or more, more preferably 0.5 hours or more, stillmore preferably 1.0 hour or more, and yet still more preferably 1.5hours or more.<39> The method for producing the asphalt composition as set forth inany of <34> to <38>, wherein a mixing time of asphalt and cellulose ispreferably 10 hours or less, more preferably 7 hours or less, still morepreferably 5 hours or less, and yet still more preferably 3 hours orless.<40> The method for producing the asphalt composition as set forth inany of <34> to <39>, wherein a mixing time of asphalt and cellulose ispreferably 0.1 hour or more and 10 hours or less, more preferably 0.5hours or more and 7 hours or less, still more preferably 1.0 hour ormore and 5 hours or less, and yet still more preferably 1.5 hours ormore and 3 hours or less.<41> The method for producing the asphalt composition as set forth inany of <15> to <19>, wherein the cellulose is a surface-hydrophobizedcellulose, and the surface-hydrophobized cellulose is produced by a stepof adding a surface hydrophobizing agent to cellulose having acrystallization index of more than 50%, followed by mixing andpulverizing, thereby controlling the crystallization index to 50% orless.<42> An additive for asphalt, including cellulose having acrystallization index of 50% or less.<43> The additive for asphalt as set forth in <42>, wherein the additivefor asphalt is used upon being mixed with asphalt, and the additionamount of the additive for asphalt is preferably 0.01 part by mass ormore, more preferably 0.03 parts by mass or more, still more preferably0.1 part by mass or more, and yet still more preferably 0.3 parts bymass or more based on 100 parts by mass of asphalt.<44> The additive for asphalt as set forth in <42> or <43>, wherein theadditive for asphalt is used upon being mixed with asphalt, and theaddition amount of the additive for asphalt is preferably 10 parts bymass or less, more preferably 8 parts by mass or less, still morepreferably 6 parts by mass or less, and yet still more preferably 4parts by mass or less based on 100 parts by mass of asphalt.<45> The additive for asphalt as set forth in any of <42> to <44>,wherein the additive for asphalt is used upon being mixed with asphalt,and the addition amount of the additive for asphalt is preferably 0.01part by mass or more and 10 parts by mass or less, more preferably 0.03parts by mass or more and 8 parts by mass or less, still more preferably0.1 part by mass or more and 6 parts by mass or less, yet still morepreferably 0.3 parts by mass or more and 4 parts by mass or less, evenyet still more preferably 1 part by mass or more and 4 parts by mass orless, and even still more preferably 2 parts by mass or more and 4 partsby mass or less based on 100 parts by mass of asphalt.<46> The additive for asphalt as set forth in any of <42> to <45>,wherein a crystallization index of the cellulose is preferably 45% orless, and more preferably 40% or less.<47> The additive for asphalt as set forth in any of <42> to <46>,wherein a crystallization index of the cellulose is preferably 1% ormore, and more preferably 10% or more.<48> The additive for asphalt as set forth in any of <42> to <47>,wherein a crystallization index of the cellulose is preferably 1% ormore and 45% or less, and more preferably 10% or more and 40% or less.

EXAMPLES

Respective physical values were measured and evaluated by the followingmethods.

In the following Examples and Comparative Examples, the terms “parts”and “%” are on a mass basis unless otherwise indicated.

(1) Measurement of Moisture Content

The moisture content of each of pulp and powdery cellulose was measuredwith an infrared moisture analyzer (“MOC-120H”, manufactured by ShimadzuCorporation). Using 5 g of a sample for a single measurement, the samplewas levelled and measured at a temperature of 120° C., and a point atwhich a rate of change in mass for 30 seconds reached 0.05% or less wasdefined as an end point of the measurement. The measured moisturecontent was expressed in terms of a mass % relative to the cellulose,thereby defining each moisture content.

(2) Calculation of Crystallization Index

An X-ray diffraction intensity of powdery cellulose was measured with anX-ray diffractometer (“MiniFlex II”, manufactured by Rigaku Corporation)under the following condition, and a crystallization index of the type Icellulose on a basis of the aforementioned calculation expression (1).

The measurement was performed under the following condition: X-raysource: Cu/Kα-radiation, tube voltage: 30 kV, tube current: 15 mA,measuring range: diffraction angle 2θ=5 to 35°, scan speed of X-rays:40°/min. The sample for measurement was prepared by compressing a pellethaving an area of 320 mm² and a thickness of 1 mm.

(3) Measurement of Volume Medial Particle Diameter (Median Diameter,D50)

The volume medial particle diameter (median diameter, D50) of thepowdery cellulose was measured with a laser diffraction/scatteringparticle size distribution measuring apparatus (“LS13 320”, manufacturedby Beckman Coulter, Inc.) by means of a dry method (tornado system).Specifically, 20 mL of the powdery cellulose was charged in a cell andsucked to undergo the measurement.

(4) Measurement of Viscoelasticity (G*, sin δ)

The measurement of viscoelasticity was performed with a rheometer MCR301(manufactured by Anton Paar GmbH). The measurement was performed underthe following condition: plate diameter: 25 mm, frequency: 1.6 Hz, shearstrain: 1.0%. Specifically, a test thickness (gap) was set to 1 mm, andG* (complex modulus of elasticity) and sin δ at 60° C. and 0° C. wereobtained while cooling from 100° C. to 0° C. at a rate of 4° C./min.

Production Method 1 (Production of Amorphous Cellulose) (1) CuttingTreatment

A sheet-form wood pulp (“Biofloc HV+”, manufactured by Tembec, Inc.,crystallization index: 82%, moisture content: 8.5% by mass) as acellulose-containing raw material was cut in a chip form having a sizeof about 3 mm×1.5 mm×1 mm by using a cutting machine.

(2) Drying Treatment

The pulp obtained by the above cutting treatment (1) was dried through acontinuous treatment with a twin-screw horizontal agitated dryer (atwin-screw paddle dryer: “NPD-3W (1/2)”, manufactured by Nara MachineryCo., Ltd.). Steam at 150° C. was used as a heating medium of the dryer,and the treatment was performed at a supply rate of the pulp of 45 kg/hunder atmospheric pressure. The moisture content of the pulp afterdrying was 0.3%.

(3) Decrystallization Treatment of Cellulose

The dry pulp obtained by the above drying treatment (2) was coarselypulverized with a continuous-type vibration mill (“Vibro mill,YAMT-200”, manufactured by Uras Techno Co., Ltd., capacities of firstand second pulverization chambers: 112 L, made by stainless steel). Thefirst and second pulverization chambers were each accommodated with 80stainless steel-made round-form pulverizing media (rods) having adiameter of 30 mm and a length of 1,300 mm. The dry pulp was supplied ata rate of 20.0 kg/h under a condition of the continuous-type vibrationmill at a vibration number of 16.7 Hz and an amplitude of 13.4 mm.

(4) Particle Diameter Reduction Treatment of Cellulose

The amorphous cellulose obtained in the above decrystallizationtreatment (3) was subjected to particle diameter reduction with ahigh-speed rotary pulverizer (a product name: “ATOMIZER AIIW-5 Type”,manufactured by DALTON Corporation). A screen with an opening of 1.0 mmwas installed; the pulverizer was driven at a rotor peripheral speed of8,000 rpm and at a rate of 50 m/s; the amorphous cellulose was suppliedfrom a raw material supply part at the same supply rate as that in thedecrystallization treatment; and the amorphous cellulose was recoveredfrom a discharge port. In the resulting amorphous cellulose, themoisture content was 2.5% by mass, the crystallization index was 0%, andthe volume medial particle diameter (median diameter, D50) was 62 μm.

The treatments (1) to (4) were carried out in continuous manner.

Production Example 2 (Production of Surface-Hydrophobized Cellulose 1)(1) Cutting Treatment

A sheet-form wood pulp (“Biofloc HV+”, manufactured by Tembec, Inc.,crystallization index: 82%, moisture content: 8.5% by mass) as acellulose-containing raw material was cut in a chip form having a sizeof about 3 mm×1.5 mm×1 mm by using a cutting machine.

(2) Drying Treatment

The pulp obtained by the above cutting treatment (1) was dried through acontinuous treatment with a twin-screw horizontal agitated dryer (atwin-screw paddle dryer: “NPD-3W (1/2)”, manufactured by Nara MachineryCo., Ltd.). Steam at 150° C. was used as a heating medium of the dryer,and the treatment was performed at a supply rate of the pulp of 45 kg/hunder atmospheric pressure. The moisture content of the pulp afterdrying was 0.3%.

(3) Decrystallization Treatment of Cellulose

The dry pulp obtained by the above drying treatment (2) and a surfacehydrophobizing agent were mixed and pulverized with a batch-typevibration mill (“Vibration Mill, FV-10”, manufactured by Chuo KakohkiCo., Ltd., capacity of pulverization chamber: 33 L, made by stainlesssteel). The pulverization chamber was accommodated with 63 stainlesssteel-made round-form pulverizing media (rods) having a diameter of 30mm and a length of 510 mm. 736 g of the dry pulp and 184 g of thesurface hydrophobizing agent (“UMEX 1001”, manufactured by SanyoChemical Industries, Ltd., maleic anhydride-modified polypropylene, acidvalue: 26 mgKOH/g, molecular weight Mw=45,000) were charged and thenmixed and pulverized (pulverization time: 10 minutes) under a conditionof the batch-type vibration mill at a vibration number of 20 Hz and anamplitude of 8 mm.

(4) Particle Diameter Reduction Treatment of Cellulose

The surface-hydrophobized cellulose obtained by the above mixing andpulverizing treatment (3) was subjected to particle diameter reductionwith a high-speed rotary pulverizer (a product name: “Free PulverizerM-3 Type”, manufactured by Nara Machinery Co., Ltd.). A screen with anopening of 1.0 mm was installed; the pulverizer was driven at a rotorperipheral speed of 7,700 rpm and at a rate of 81 m/s; thesurface-hydrophobized cellulose was supplied from a raw material supplypart at a rate of 18 kg/h; and the surface-hydrophobized cellulose wasrecovered from a discharge port. In the resulting surface-hydrophobizedcellulose, the moisture content was 1.0% by mass, the crystallizationindex was 37%, and the volume medial particle diameter (median diameter,D50) was 44 μm.

The treatments (1) to (2) were carried out in a continuous manner, andthe treatments (3) to (4) were carried out in a batch manner.

Production Example 3 (Production of Surface-Hydrophobized Cellulose 2)

A surface-hydrophobized cellulose 2 was obtained in the same manner asin Production Example 2, except for changing the mixing and pulverizingtime to 30 minutes. In the resulting surface-hydrophobized cellulose,the crystallization index was 1.7%, and the volume medial particlediameter (D50) was 63 μm.

Production Example 4 (Production of Surface-Hydrophobized Cellulose 3)

A surface-hydrophobized cellulose 3 was obtained in the same manner asin Production Example 3, except for changing the amount of the surfacehydrophobizing agent (“UMEX 1001”, manufactured by Sanyo ChemicalIndustries, Ltd., maleic anhydride-modified polypropylene, acid value:26 mgKOH/g, molecular weight Mw=45,000) to 242.9 g. In the resultingsurface-hydrophobized cellulose, the crystallization index was 17%, andthe volume medial particle diameter (D50) was 72 μm.

Production Example 5 (Production of Surface-Hydrophobized Cellulose 4)

A surface-hydrophobized cellulose 4 was obtained in the same manner asin Production Example 2, except for changing the surface hydrophobizingagent to 36.8 g of Z-6011 (3-aminopropyl triethoxysilane, manufacturedby Dow Toray Co., Ltd.). In the resulting surface-hydrophobizedcellulose, the crystallization index was 49%, and the volume medialparticle diameter (D50) was 57 μm.

Production Example 6 (Production of Polymer-Modified Asphalt)

To 100 parts of the straight asphalt which had been previously heated to180° C., 1 part of “UMEX 1001” (manufactured by Sanyo ChemicalIndustries, Ltd., maleic anhydride-modified polypropylene, acid value:26 mgKOH/g, molecular weight Mw=45,000) was added and agitated with ahomomixer (T.K. Robomix: a T.K. homomixer specification, manufactured byPRIMIX Corporation) for 5 minutes under a condition at a rotation numberof 8,000 rpm.

Example 1 (Mixing of Straight Asphalt and Amorphous Cellulose)

To 100 parts of the straight asphalt which had been previously heated to180° C., 3 parts of the amorphous cellulose prepared in ProductionExample 1 was added and agitated with a homomixer for 2 hours under acondition at a rotation number of 8,000 rpm and an inner temperature of180° C.

Example 2 (Mixing of Polymer-Modified Asphalt and Amorphous Cellulose)

To 100 parts of the polymer-modified asphalt prepared in ProductionExample 6, 3 parts of the amorphous cellulose prepared in ProductionExample 1 was added and agitated under the same condition as in Example1.

Example 3 (Mixing of Straight Asphalt and Surface-HydrophobizedCellulose 1)

To 100 parts of the straight asphalt which had been previously heated to180° C., 3 parts of the surface-hydrophobized cellulose 1 prepared inProduction Example 2 was added and agitated under the same condition asin Production Example 1.

Example 4 (Mixing of Polymer-Modified Asphalt and Surface-HydrophobizedCellulose 1)

To 100 parts of the polymer-modified asphalt prepared in ProductionExample 6, 3 parts of the surface-hydrophobized cellulose 1 prepared inProduction Example 2 was added and agitated under the same condition asin Example 1.

Example 5 (Mixing of Straight Asphalt and Surface-HydrophobizedCellulose 1)

To 100 parts of the straight asphalt which had been previously heated to180° C., 0.3 parts of the surface-hydrophobized cellulose 1 prepared inProduction Example 2 was added and agitated under the same condition asin Production Example 1.

Example 6 (Mixing of Straight Asphalt and Surface-HydrophobizedCellulose 2)

To 100 parts of the straight asphalt which had been previously heated to180° C., 3 parts of the surface-hydrophobized cellulose 2 prepared inProduction Example 3 was added and agitated under the same condition asin Production Example 1.

Example 7 (Mixing of Straight Asphalt and Surface-HydrophobizedCellulose 3)

To 100 parts of the straight asphalt which had been previously heated to180° C., 3 parts of the surface-hydrophobized cellulose 3 prepared inProduction Example 4 was added and agitated under the same condition asin Production Example 1.

Example 8 (Mixing of Straight Asphalt and Surface-HydrophobizedCellulose 4)

To 100 parts of the straight asphalt which had been previously heated to180° C., 3 parts of the surface-hydrophobized cellulose 4 prepared inProduction Example 5 was added and agitated under the same condition asin Production Example 1.

Comparative Example 1

Agitation was performed under the same condition as in Example 1, exceptfor not adding the amorphous cellulose.

Comparative Example 2

Agitation was performed under the same condition as in Example 2, exceptfor not adding the amorphous cellulose.

Comparative Example 3 (Mixing of Polymer-Modified Asphalt andCrystalline Cellulose)

To 100 parts of the polymer-modified asphalt prepared in ProductionExample 6, 3 parts of crystalline cellulose (“KC FLOCK W-50GK”,manufactured by Nippon Paper Industries Co., Ltd., crystallizationindex: 62%, median diameter: 45 μm) and agitated under the samecondition as in Example 1.

Comparative Example 4

Using, as the raw material cellulose, one obtained by furtherpulverizing the chip produced by the cutting treatment of ProductionExample 1 in a fibrous form by using a coffee mill, subsequentlyrepeating an operation of pulverization with a planetary ball mill (P-6Type, manufactured by Fritsch Inc., using 100 alumina balls of ϕ10 mm asmedia, total of pulverized products: 40 g) at a rotation number of 250rpm for 50 minutes and stopping for 10 minutes in 24 cycles, agitationwas performed under the same condition as in Example 1.

With respect to the asphalt compositions obtained in the Examples andComparative Examples, G* and sin δ were measured, and G*/sin δ and G*sinδ were calculated. The results are shown in the following Table 1.

In view of the fact that the larger the value of G*/sin δ, the largerthe plastic flow resistance is, it is evaluated that the asphaltpavement with excellent rutting resistance can be provided by theforegoing asphalt composition.

In addition, in view of the fact that the smaller the value of G*sin δ,the larger the fatigue cracking resistance is, it is evaluated that theasphalt pavement with excellent fatigue cracking resistance can beprovided by the foregoing asphalt composition.

TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 8 1 2 3 4 ChargeStraight asphalt Parts 100 100 100 100 100 100 100 100 Polymer-modifiedasphalt Parts 100 100 100 100 Amorphous cellulose Parts 3 3 3Surface-hydrophobized cellulose 1 Parts 3 3 0.3 (Cellulose/UMEX =100/25) Surface-hydrophobized cellulose 2 Parts 3 (Cellulose/UMEX =100/25) Surface-hydrophobized cellulose 3 Parts 3 (Cellulose/UMEX =100/33) Surface-hydrophobized cellulose 4 Parts 3 (Cellulose/Silanecoupling agent = 100/5) Crystalline cellulose Parts 3 Cellulose Volumemedial particle diameter μm 62 62 44 44 44 63 72 57 — — 49 33 (mediandiameter, D50) Crystallization index % 0 0 37 37 37 1.7 17 49 — — 62 53Agitation Temperature ° C. 180 — — 180 Time min 120 — — 120Viscoelasticity G*/sinδ (60° C.) kPa 4.4 6.6 5.4 7.0 5.1 5.4 7.8 5.7 4.04.2 4.9 4.2 G* × sinδ (0° C.) MPa 4.4 4.2 4.1 4.1 5.0 4.9 5.0 4.8 5.45.1 5.1 5.3

It is noted from the results of Table 1 that in accordance with theasphalt compositions of the Examples, an asphalt pavement in which theoccurrence of rutting and fatigue cracking is inhibited is obtained, ascompared with the asphalt compositions of the Comparative Examples.

1. An asphalt composition comprising asphalt and cellulose, wherein thecontent of the cellulose is 0.01 part by mass or more and 10 parts bymass or less based on 100 parts by mass of the asphalt, and acrystallization index of the cellulose is 50% or less.
 2. The asphaltcomposition according to claim 1, wherein the asphalt is selected from astraight asphalt and a polymer-modified asphalt.
 3. The asphaltcomposition according to claim 1, wherein the asphalt is apolymer-modified asphalt containing a polymer having a polar group and apolyolefin chain.
 4. The asphalt composition according to claim 3,wherein the polymer having a polar group and a polyolefin chain ismaleic anhydride-modified polypropylene or maleic anhydride-modifiedpolyethylene.
 5. The asphalt composition according to claim 1, whereinthe cellulose is a surface-hydrophobized cellulose.
 6. The asphaltcomposition according to claim 5, wherein the treatment amount with asurface hydrophobizing agent is 1 part by mass or more and 100 parts bymass or less based on 100 parts by mass of the untreated cellulose. 7.The asphalt composition according to claim 5, wherein thesurface-hydrophobized cellulose is cellulose subjected to a surfacetreatment with at least one surface hydrophobizing agent selected from asilane-based coupling agent, a titanate-based coupling agent, analuminum-based coupling agent, and a polymer having a polar group and apolyolefin chain.
 8. The asphalt composition according to claim 1,wherein the asphalt is a polymer-modified asphalt, wherein the amount ofa modifier added to a straight asphalt is 0.1 part by mass or more and20 parts by mass or less based on 100 parts by mass of the straightasphalt.
 9. The asphalt composition according to claim 1, wherein amedian diameter of the cellulose is 5 μm or more and 200 μm or less. 10.(canceled)
 11. A method for producing the asphalt composition accordingto claim 1, comprising a step of mixing asphalt and cellulose having acrystallization index of 50% or less.
 12. The method for producing theasphalt composition according to claim 11, wherein the cellulose is asurface-hydrophobized cellulose, and the surface-hydrophobized celluloseis produced by a method comprising a decrystallization step of adding asurface hydrophobizing agent to cellulose having a crystallization indexof more than 50%, followed by mixing and pulverizing, therebycontrolling the crystallization index to 50% or less.
 13. An additivefor asphalt, comprising cellulose having a crystallization index of 50%or less.
 14. The asphalt composition according to claim 3, wherein thepolar group is an (anhydrous) carboxylic acid group or an epoxy group.15. The asphalt composition according to claim 5, wherein thesurface-hydrophobized cellulose is subjected to a surface treatment by ahydrophobizing agent, the hydrophobizing agent is a polymer having apolar group and a polyolefin chain, and the polar group is an(anhydrous) carboxylic acid group or an epoxy group.
 16. The asphaltcomposition according to claim 1, wherein the asphalt is apolymer-modified asphalt having a polar group and a polyolefin chain,the cellulose is a surface-hydrophobized cellulose that is subjected toa surface treatment with a hydrophobizing agent, and the hydrophobizingagent is a polymer having a polar group and a polyolefin chain.
 17. Theasphalt composition according to claim 1, wherein the asphalt is apolymer-modified asphalt containing a maleic anhydride-modifiedpolypropylene, and the cellulose is a surface-hydrophobized cellulosethat is subjected to a surface treatment with the maleicanhydride-modified polypropylene.
 18. The method for producing theasphalt composition according to claim 12, wherein a pulverizer is usedin the decrystallization step, which is a medium-type pulverizer.
 19. Aroad pavement comprising an asphalt composition containing asphalt andcellulose, wherein the content of the cellulose is 0.01 part by mass ormore and 10 parts by mass or less based on 100 parts by mass of theasphalt, and a crystallization index of the cellulose is 50% or less.